FIG. 1 illustrates a conventional MOSFET 10. The device is formed in a p-well or an n-well 11 formed in a silicon substrate (not shown). A channel 12 is then doped by, for example, ion implantation. A high dielectric constant (k) film 15 is then formed over the device by chemical vapor deposition (CVD) or sputtering. The gate, typically poly silicon or metal, is then formed over the high k film. Portions of the gate and the high k film are then etched away to expose source/drain regions 13, which are then doped.
The device is annealed, typically at about 1100xc2x0 C., to activate the p- and n-type dopants. During the high temperature anneal, the channel region 12 and the high k layer 15 react to form an interfacial layer 14. The interfacial layer and the high k film together have a lower capacitance than the high k film alone. The reduced capacitance caused by interfacial layer 14 reduces the driving current of the device and thereby reduces the operating speed of the device.
In accordance with a first embodiment of the invention, a MOSFET includes a well, a channel formed in the well, a high K layer overlying the channel, a buffer layer overlying the high k layer, a gate overlying the buffer layer, a blocking layer overlying the gate and two source/drain regions. In some embodiments the high k layer is an epitaxial metal oxide. In embodiments the buffer and blocking layers are epitaxial silicon. In some embodiments the gate and the source/drain regions are amorphous silicon germanium. In accordance with another embodiment of the invention, a MOSFET includes a well, a channel formed in the well, a high K layer overlying the channel, a metal gate overlying the high k layer, and two silicon germanium source/drain regions.